1. Field of the Invention
The present invention relates to a system and method for providing digital images of a microscope specimen, which images can be displayed on a display screen to resemble the images viewed through a microscope.
2. Description of the Related Art
The use of digital images of a microscope specimen, often referred to as “virtual microscope images”, is increasingly common in the field of diagnostic pathology, particular for remote diagnosis and training. The digital images of the specimen are typically acquired by “scanning” the specimen using a microscopy imaging system comprising a computer controlled microscope and digital camera, at one or more magnifications/resolutions.
For example, a method of acquiring digital microscope images is disclosed in EP-A-0 994 433 in the name of the present applicant. In this method, a series of adjacent specimen images is acquired from a microscope using a digital camera. In particular, a microscope stage, holding the specimen slide, is advanced in stepwise fashion, under computer control, to position the specimen within the microscope for each captured image, so as to obtain adjacent field of view images of the complete specimen. The image data for the individual, adjacent, field of view images is processed to produce data for an image of the complete specimen for viewing on a display screen.
As disclosed in EP-A-0 994 433, a focusing system including a piezo-electric driver is typically used to adjust the position of the objective lens of the microscope so as to maintain a constant sharp focus for the specimen images during the scan. This ensures that the acquired images, when assembled together, produce a sharp image for the complete specimen, essentially in a single optical plane.
Images of a specimen focused in a single optical plane are sufficient for pathologists to perform diagnosis in cases where the biological specimen is relatively thin and uniform across the sample. However, for certain types of specimen sample, there may be areas where the specimen is thicker and non-uniform. For example, cytology samples may include areas or clumps of overlapping cells. A pathologist viewing such a specimen using a conventional microscope would typically wish to change the focus of the microscope to view such a specimen at different levels, i.e. in different optical planes of the specimen. By adjusting the focus, the pathologist is able to view not only the uppermost cells but also underlying cells within the clump.
As is well known in the art, the ability to achieve sharply focused images at different levels within a specimen (i.e. in different optical planes of an object) is dependent upon the depth of field and the depth of focus of the microscope.
It would be desirable to provide a pathologist with the same ability using virtual microscope images. In particular, it would desirable to provide a pathologist with the ability to view digital microscope images of a specimen at different levels within the specimen.